Investigation on structural, dielectric, and impedance characteristics of Zr-modified NaNbO3 ceramics at elevated temperature

NaNb1−xZrxO3 (NZr) ceramics with 0≤x≤0.15 are prepared via solid-state reaction route. Structural, microstructural, and electronic state investigations of NZr samples were performed using X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), and X-ray photoelectron spectroscopy (XPS), respectively. Rietveld refinement reveals that NZr samples crystallize in the orthorhombic phase similar to room temperature Pbma phase of NaNbO3. Minor quantities of ZrO2 are detected for higher NZr-composition, which suppress the grain growth of NZr ceramics. XPS reveals that small amount of Zr substitution in NaNbO3 also creates an ambiance of unbalanced charge neutrality. The dielectric characteristics of NZr samples are investigated from −190 to 450 °C temperature range in frequency window 1 KHz–1 MHz for both the heating and cooling cycles. A clear thermal hysteresis loop is obtained in each composition and the observed anomaly corresponds to P (AFE) - R (AFE) polymorphic phase transition. As x grows, ɛ′ (T) becomes more dispersive and strongly depend on applied field. The activation energy obtained from the analysis of Arrhenius relation indicates that the oxygen vacancies are responsible for conduction process of the material. Impedance analysis confirms the NTCR behavior and non-Debye relaxation of the material.